This invention relates to a system of stabilising soil slopes and a method related thereto.
On steep slopes having generally less than 45 degrees of inclination to the horizontal, the prevention of soil erosion is typically accomplished by planting vegetation on the surface of the slope. The roots of the vegetation secure the soil at the surface. Vegetation alone however does not prevent large shifts of the soil.
The use of nails and other forms of anchors is known for stabilising soil on vertical or near vertical faces. Generally these nails are installed with shotcrete or precast concrete facings between the nails during the formation of the faces for retaining the soil between the nails. There is no known precedent for utilising nails on existing slopes having an inclination of less than 45 degrees.
It is an object of the present invention to provide a stabilisation system for soil slopes which incorporates internal soil slope stability with the prevention of surface soil erosion.
According to one aspect of the present invention there is provided a method for stabilising soil within a slope having generally less than 45 degrees of inclination from horizontal, said method comprising:
penetrating a plurality of soil nails into the soil; and
establishing vegetation adjacent a top surface of the soil, the vegetation being arranged to generate roots which penetrate through the surface into the soil.
The use of soil nails provides internal soil stability to a slope or embankment by penetrating the nail through the soil past an existing or potential failure plane. The soil nails extend transversely to existing or potential failure planes to resist internal shearing forces within the slope of soil. A cover of vegetation established onto the surface of the soil provides further stability to the slope. The vegetation established at the surface of the slope prevents erosion or shallow failure near the surface of the slopes. Additional retaining members may also be mounted along the crest of the slope by anchoring the retaining members to the slope with the soil nails to further inhibit soil erosion and shallow failure at the crest.
A biotechnical facing may be established by providing a geosynthetic layer comprising a mat, mesh or fibrous material placed over or near the soil surface before or after seeding or planting such that the vegetation is stabilised on the surface of the slope for retaining the soil adjacent the surface of the slope.
A retaining member can be mounted adjacent a crest of the slope to extend transversely thereto. The retaining member further inhibits soil erosion and shallow failure at the crest.
The retaining member may comprise an elongate plate member, wherein the method includes orienting the plate member to extend substantially perpendicularly to the surface of the soil and to project outwardly therefrom.
The method may further include filling a space defined between the retaining member and a crest of the slope with soil. The crest of the slope thus provides a broad stable base for supporting for example a roadway or a railway thereon.
The retaining member may be anchored with a plurality of soil nails coupled thereto, wherein each soil nail is penetrated into the slope.
A plate member may be mounted on each soil nail adjacent one end thereof and orienting the soil nails before penetration into the slope so that plate extends transversely to the slope.
The plate members on the soil nails are preferably oriented to lie in a substantially common plane therewith such that the plate members extend perpendicularly to the slope when the soil nails are penetrated perpendicularly into the surface of the slope.
According to a further aspect of the present invention there is provided a stabilisation system for stabilising soil within a slope having generally less than 45 degrees of inclination from horizontal, said system comprising:
a plurality of soil nails, each having a soil penetrating end for penetrating into the soil and a surface engaging end for engaging a top surface of the soil; and
a biotechnical facing arranged to cover the top surface of the soil.
The biotechnical facing preferably comprises a mass of organic fibres having a root structure arranged to penetrate into the soil.
There may be provided a geosynthetic layer comprising a mat, mesh or fibrous material arranged on or near the surface to further reinforce the surface and assist in establishing the mass of organic fibres thereon.
A retaining wall structure may be mounted on the slope to extend longitudinally along a crest of the slope.
In one arrangement of the present invention, the retaining wall comprises:
a pair of retaining members mounted spaced apart on a crest of the slope to extend longitudinally with the crest; and
a plurality of cross members, each being connected between the pair of retaining members for mounting the retaining members parallel and spaced apart in relation to one another.
Alternatively the retaining wall structure may comprise an elongate plate member oriented perpendicularly to the surface of the soil to project outwardly therefrom.
There may be provided a filler material located within a spaced defined between the retaining wall structure and the crest of the slope. The filler material may comprise gravel or the like to provide a stable base while permitting drainage therethrough at the crest of the slope.
There may be provided a plurality of soil nails which are penetrated in the soil and coupled to the retaining wall structure for anchoring the retaining wall structure adjacent the crest of the slope.
There may be provided a soil retaining plate member mounted on the surface engaging end of the each soil nail for engaging and retaining the soil adjacent the surface of the slope.
The soil retaining plates are preferably mounted on each soil nail to lie in a substantially common plane therewith such that the plates are oriented perpendicularly to the slope when the soil nails are penetrated into the soil perpendicularly to the surface thereof.